Use of phytoremediation techniques for elimination of lead from polluted soils

The effect of chelating agent – EDTA (ethylene-diamine-tetra-acetic acid) was used for induced phytoextraction to increase intensity of lead transfer from roots to aboveground parts of garden pea. Pot experiments with contaminated soil substrata (50 mg Pb.kg-1 and 100 mg Pb.kg-1) were established for experimental purposes in growth chamber. The results showed that application of 5 and 10 mmol EDTA.kg-1 to experimental variants with 100 mg Pb.kg-1 doubled the increase of lead uptake by pea roots in comparison with variants without EDTA addition, which was statistically confirmed. Intensive lead transfer was observed from roots to aboveground parts of pea after application of 5 and 10 mmol EDTA.kg-1 in variant with 50 mg Pb.kg-1 (40-fold increase), as well as in variant with 100 mg Pb.kg-1 (17-fold increase). The results showed that induced phytoextraction can improve the mobility of lead from soil to plant roots. Application of 5 mmol EDTA.kg-1 resulted to 40-fold increase of lead transfer to green plant parts, despite the fact, that garden pea does not belong to conventional metal hyperaccumulating plant species. Following the results, pea could be used for decontamination of arable soil. The optimal EDTA concentration seems to be 5 mmol.kg-1. Therefore, application of 10 mmol EDTA.kg-1 decreased root mass about 55%, which resulted to decrease the intensity of lead uptake.

Between the devil and the deep blue sea: herbivory induces foraging for and uptake of cadmium in a metal hyperaccumulating plant

Plants have been shown to change their foraging behaviour in response to resource heterogeneity. However, an unexplored hypothesis is that foraging could be induced by environmental stressors, such as herbivory, which might increase the demand for particular resources, such as those required for herbivore defence. This study examined the way simulated herbivory affects both root foraging for and uptake of cadmium (Cd), in the metal-hyperaccumulating plant Arabidopsis halleri , which uses this heavy metal as herbivore defence. Simulated herbivory elicited enhanced relative allocation of roots to Cd-rich patches as well as enhanced Cd uptake, and these responses were exhibited particularly by plants from non-metalliferous origin, which have lower metal tolerance. By contrast, plants from a metalliferous origin, which are more tolerant to Cd, did not show any preference in root allocation, yet enhanced Cd sharing between ramets when exposed to herbivory. These results suggest that foraging for heavy metals, as well as their uptake and clonal-sharing, could be stimulated in A. halleri by herbivory impact. Our study provides first support for the idea that herbivory can induce not only defence responses in plants but also affect their foraging, resource uptake and clonal sharing responses.

The Cardamine enshiensis genome reveals whole genome duplication and insight into selenium hyperaccumulation and tolerance

Cardamine enshiensis is a well-known selenium (Se)-hyperaccumulating plant. Se is an essential trace element associated with many health benefits. Despite its critical importance, genomic information of this species is limited. Here, we report a chromosome-level genome assembly of C. enshiensis, which consists of 443.4 Mb in 16 chromosomes with a scaffold N50 of 24 Mb. To elucidate the mechanism of Se tolerance and hyperaccumulation in C. enshiensis, we generated and analyzed a dataset encompassing genomes, transcriptomes, and metabolomes. The results reveal that flavonoid, glutathione, and lignin biosynthetic pathways may play important roles in protecting C. enshiensis from stress induced by Se. Hi-C analysis of chromatin interaction patterns showed that the chromatin of C. enshiensis is partitioned into A and B compartments, and strong interactions between the two telomeres of each chromosome were correlated with histone modifications, epigenetic markers, DNA methylation, and RNA abundance. Se supplementation could affect the 3D chromatin architecture of C. enshiensis at the compartment level. Genes with compartment changes after Se treatment were involved in selenocompound metabolism, and genes in regions with topologically associated domain insulation participated in cellular responses to Se, Se binding, and flavonoid biosynthesis. This multiomics research provides molecular insight into the mechanism underlying Se tolerance and hyperaccumulation in C. enshiensis.

Frenemies: Interactions between Rhizospheric Bacteria and Fungi from Metalliferous Soils

Is it possible to improve the efficiency of bioremediation technologies? The use of mixed cultures of bacteria and fungi inoculated at the rhizosphere level could promote the growth of the associated hyperaccumulating plant species and increase the absorption of metals in polluted soils, broadening new horizons on bioremediation purposes. This work investigates interactions between Ni-tolerant plant growth-promoting bacteria and fungi (BF) isolated from the rhizosphere of a hyperaccumulating plant. The aim is to select microbial consortia with synergistic activity to be used in integrated bioremediation protocols. Pseudomonas fluorescens (Pf), Streptomyces vinaceus (Sv) Penicillium ochrochloron (Po), and Trichoderma harzianum group (Th) were tested in mixes (Po-Sv, Po-Pf, Th-Pf, and Th-Sv). These strains were submitted to tests (agar overlay, agar plug, and distance growth co-growth tests), tailored for this aim, on Czapek yeast agar (CYA) and tryptic soy agar (TSA) media and incubated at 26 ± 1 °C for 10 days. BF growth, shape of colonies, area covered on plate, and inhibition capacity were evaluated. Most BF strains still exhibit their typical characters and the colonies separately persisted without inhibition (as Po-Sv) or with reciprocal confinement (as Th-Sv and Th-Pf). Even if apparently inhibited, the Po-Pf mix really merged, thus obtaining morphological traits representing a synergic co-growth, where both strains reached together the maturation phase and developed a sort of mixed biofilm. Indeed, bacterial colonies surround the mature fungal structures adhering to them without any growth inhibition. First data from in vivo experimentation with Po and Pf inocula in pot with metalliferous soils and hyperaccumulator plants showed their beneficial effect on plant growth. However, there is a lack of information regarding the effective co-growth between bacteria and fungi. Indeed, several studies, which directly apply the co-inoculum, do not consider suitable microorganisms consortia. Synergic rhizosphere BFs open new scenarios for plant growth promotion and soil bioremediation.

Thallium uptake/tolerance in a model (hyper)accumulating plant: Effect of extreme contaminant loads

Thallium (Tl) is a toxic trace element with a highly negative effect on the environment. For phytoextraction purposes, it is important to know the limitations of plant growth. In this study, we conducted experiments with a model Tl-hyperaccumulating plant (Sinapis alba L., white mustard) to better understand the plant tolerance and/or associated detoxification mechanisms under extreme Tl doses (accumulative 0.7/1.4 mg Tl, in total). Both the hydroponic/semi-hydroponic (artificial soil) cultivation variants were studied in detail. The Tl bioaccumulation potential for the tested plant reached up to 1% of the total supplied Tl amount. Furthermore, it was revealed that the plants grown in the soil-like system did not tolerate Tl concentrations in nutrient solutions higher than ~1 mg/L, i.e., wilting symptoms were evident. Surprisingly, for the plants grown in hydroponic solutions, the tolerable Tl concentration was by contrast at least 2-times higher (≥ 2 mg Tl/L), presumably mimicking the K biochemistry. The obtained hydroponic/semi-hydroponic phytoextraction data can serve, in combination, as a model for plant-assisted remediation of soils or mining/processing wastes enriched in Tl, or possibly for environmental cycling of Tl in general.

Corrigendum in the article: Extraction of ammonium nickel sulfate hexahydrate by hydrometallurgical process from the hyperaccumulating plant Odontarrhena muralis - case study from Serbia

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Extraction of ammonium nickel sulfate hexahydrate by hydrometallurgical process from the hyperaccumulating plant Odontarrhena muralis – case study from Serbia

Phytomining is a new promising technique that is based on using hyperaccumulating plants which biomass is utilized as a bio-ore for metal extraction. The Ni-hyperaccumulating species Odontarrhena muralis is widely distributed on ultramafic soils in Serbia, and could be a promising candidate for Ni agromining. In the present study, efficiency of a hydrometallurgical process for Ni recovery using biomass of O. muralis wild population through the synthesis of Ni salts from plant ash in the form of ammonium nickel sulfate hexahydrate, Ni(NH4)2(SO4)2 6H2O ? (ANSH) was assessed. The average Ni content in the plant from ultramafic sites in West Serbia was up to 3.300 g kg-1. The mass yield of ANSH crystals from the crude ash was ~12 % with the average purity of 73 % were obtained. By optimizing the purification process before precipitation of ANSH crystals, it is possible to obtain salt crystals of higher purity, which increases the economic profitability of this process. The results of this preliminary study on wild population of O. muralis show the increased potential for implementation of phytomining practices as an alternative way of Ni extraction on ultramafic sites in Serbia.